DESCRIPTION

Gawk
is the GNU Project's implementation of the AWK programming language.
It conforms to the definition of the language in
the POSIX 1003.2 Command Language And Utilities Standard.
This version in turn is based on the description in
The AWK Programming Language,
by Aho, Kernighan, and Weinberger,
with the additional features found in the System V Release 4 version
of UNIXawk.
Gawk
also provides more recent Bell Laboratories
awk
extensions, and a number of GNU-specific extensions.

Pgawk
is the profiling version of
gawk.
It is identical in every way to
gawk,
except that programs run more slowly,
and it automatically produces an execution profile in the file
awkprof.out
when done.
See the
--profile
option, below.

The command line consists of options to
gawk
itself, the AWK program text (if not supplied via the
-f
or
--file
options), and values to be made
available in the
ARGC
and
ARGV
pre-defined AWK variables.

OPTION FORMAT

Gawk
options may be either traditional POSIX one letter options,
or GNU style long options. POSIX options start with a single ``-'',
while long options start with ``--''.
Long options are provided for both GNU-specific features and
for POSIX-mandated features.

Following the POSIX standard,
gawk-specific
options are supplied via arguments to the
-W
option. Multiple
-W
options may be supplied
Each
-W
option has a corresponding long option, as detailed below.
Arguments to long options are either joined with the option
by an
=
sign, with no intervening spaces, or they may be provided in the
next command line argument.
Long options may be abbreviated, as long as the abbreviation
remains unique.

OPTIONS

Gawk
accepts the following options, listed alphabetically.

-F fs

--field-separator fs
Use
fs
for the input field separator (the value of the
FS
predefined
variable).

-v var=val

--assign var=val
Assign the value
val
to the variable
var,
before execution of the program begins.
Such variable values are available to the
BEGIN
block of an AWK program.

-f program-file

--file program-file
Read the AWK program source from the file
program-file,
instead of from the first command line argument.
Multiple
-f
(or
--file)
options may be used.

-mf NNN

-mr NNN
Set various memory limits to the value
NNN.
The
f
flag sets the maximum number of fields, and the
r
flag sets the maximum record size. These two flags and the
-m
option are from the Bell Laboratories research version of UNIXawk.
They are ignored by
gawk,
since
gawk
has no pre-defined limits.

-W compat

-W traditional

--compat

--traditional
Run in
compatibility
mode. In compatibility mode,
gawk
behaves identically to UNIXawk;
none of the GNU-specific extensions are recognized.
The use of
--traditional
is preferred over the other forms of this option.
See
GNU EXTENSIONS,
below, for more information.

-W copyleft

-W copyright

--copyleft

--copyright
Print the short version of the GNU copyright information message on
the standard output and exit successfully.

-W dump-variables[=file]

--dump-variables[=file]
Print a sorted list of global variables, their types and final values to
file.
If no
file
is provided,
gawk
uses a file named
awkvars.out
in the current directory.

Having a list of all the global variables is a good way to look for
typographical errors in your programs.
You would also use this option if you have a large program with a lot of
functions, and you want to be sure that your functions don't
inadvertently use global variables that you meant to be local.
(This is a particularly easy mistake to make with simple variable
names like
i,
j,
and so on.)

-W help

-W usage

--help

--usage
Print a relatively short summary of the available options on
the standard output.
(Per the
GNU Coding Standards,
these options cause an immediate, successful exit.)

-W lint[=fatal]

--lint[=fatal]
Provide warnings about constructs that are
dubious or non-portable to other AWK implementations.
With an optional argument of
fatal,
lint warnings become fatal errors.
This may be drastic, but its use will certainly encourage the
development of cleaner AWK programs.

-W lint-old

--lint-old
Provide warnings about constructs that are
not portable to the original version of Unix
awk.

-W gen-po

--gen-po
Scan and parse the AWK program, and generate a GNU.po
format file on standard output with entries for all localizable
strings in the program. The program itself is not executed.
See the GNUgettext
distribution for more information on
.po
files.

-W non-decimal-data

--non-decimal-data
Recognize octal and hexadecimal values in input data.
Use this option with great caution!

-W posix

--posix
This turns on
compatibility
mode, with the following additional restrictions:

*

\x
escape sequences are not recognized.

*

Only space and tab act as field separators when
FS
is set to a single space, newline does not.

*

You cannot continue lines after
?
and
:.

*

The synonym
func
for the keyword
function
is not recognized.

*

The operators
**
and
**=
cannot be used in place of
^
and
^=.

*

The
fflush()
function is not available.

-W profile[=prof_file]

--profile[=prof_file]
Send profiling data to
prof_file.
The default is
awkprof.out.
When run with
gawk,
the profile is just a ``pretty printed'' version of the program.
When run with
pgawk,
the profile contains execution counts of each statement in the program
in the left margin and function call counts for each user-defined function.

-W re-interval

--re-interval
Enable the use of
interval expressions
in regular expression matching
(see
Regular Expressions,
below).
Interval expressions were not traditionally available in the
AWK language. The POSIX standard added them, to make
awk
and
egrep
consistent with each other.
However, their use is likely
to break old AWK programs, so
gawk
only provides them if they are requested with this option, or when
--posix
is specified.

-W source program-text

--source program-text
Use
program-text
as AWK program source code.
This option allows the easy intermixing of library functions (used via the
-f
and
--file
options) with source code entered on the command line.
It is intended primarily for medium to large AWK programs used
in shell scripts.

-W version

--version
Print version information for this particular copy of
gawk
on the standard output.
This is useful mainly for knowing if the current copy of
gawk
on your system
is up to date with respect to whatever the Free Software Foundation
is distributing.
This is also useful when reporting bugs.
(Per the
GNU Coding Standards,
these options cause an immediate, successful exit.)

--
Signal the end of options. This is useful to allow further arguments to the
AWK program itself to start with a ``-''.
This is mainly for consistency with the argument parsing convention used
by most other POSIX programs.

In compatibility mode,
any other options are flagged as invalid, but are otherwise ignored.
In normal operation, as long as program text has been supplied, unknown
options are passed on to the AWK program in the
ARGV
array for processing. This is particularly useful for running AWK
programs via the ``#!'' executable interpreter mechanism.

AWK PROGRAM EXECUTION

An AWK program consists of a sequence of pattern-action statements
and optional function definitions.

pattern{ action statements }

function name(parameter list) { statements }

Gawk
first reads the program source from the
program-file(s)
if specified,
from arguments to
--source,
or from the first non-option argument on the command line.
The
-f
and
--source
options may be used multiple times on the command line.
Gawk
reads the program text as if all the
program-files
and command line source texts
had been concatenated together. This is useful for building libraries
of AWK functions, without having to include them in each new AWK
program that uses them. It also provides the ability to mix library
functions with command line programs.

The environment variable
AWKPATH
specifies a search path to use when finding source files named with
the
-f
option. If this variable does not exist, the default path is
".:/usr/local/share/awk".
(The actual directory may vary, depending upon how
gawk
was built and installed.)
If a file name given to the
-f
option contains a ``/'' character, no path search is performed.

Gawk
executes AWK programs in the following order.
First,
all variable assignments specified via the
-v
option are performed.
Next,
gawk
compiles the program into an internal form.
Then,
gawk
executes the code in the
BEGIN
block(s) (if any),
and then proceeds to read
each file named in the
ARGV
array.
If there are no files named on the command line,
gawk
reads the standard input.

If a filename on the command line has the form
var=val
it is treated as a variable assignment. The variable
var
will be assigned the value
val.
(This happens after any
BEGIN
block(s) have been run.)
Command line variable assignment
is most useful for dynamically assigning values to the variables
AWK uses to control how input is broken into fields and records.
It is also useful for controlling state if multiple passes are needed over
a single data file.

If the value of a particular element of
ARGV
is empty (""),
gawk
skips over it.

For each record in the input,
gawk
tests to see if it matches any
pattern
in the AWK program.
For each pattern that the record matches, the associated
action
is executed.
The patterns are tested in the order they occur in the program.

Finally, after all the input is exhausted,
gawk
executes the code in the
END
block(s) (if any).

VARIABLES, RECORDS AND FIELDS

AWK variables are dynamic; they come into existence when they are
first used. Their values are either floating-point numbers or strings,
or both,
depending upon how they are used. AWK also has one dimensional
arrays; arrays with multiple dimensions may be simulated.
Several pre-defined variables are set as a program
runs; these will be described as needed and summarized below.

Records

Normally, records are separated by newline characters. You can control how
records are separated by assigning values to the built-in variable
RS.
If
RS
is any single character, that character separates records.
Otherwise,
RS
is a regular expression. Text in the input that matches this
regular expression separates the record.
However, in compatibility mode,
only the first character of its string
value is used for separating records.
If
RS
is set to the null string, then records are separated by
blank lines.
When
RS
is set to the null string, the newline character always acts as
a field separator, in addition to whatever value
FS
may have.

Fields

As each input record is read,
gawk
splits the record into
fields,
using the value of the
FS
variable as the field separator.
If
FS
is a single character, fields are separated by that character.
If
FS
is the null string, then each individual character becomes a
separate field.
Otherwise,
FS
is expected to be a full regular expression.
In the special case that
FS
is a single space, fields are separated
by runs of spaces and/or tabs and/or newlines.
(But see the discussion of
--posix,
below).
NOTE:
The value of
IGNORECASE
(see below) also affects how fields are split when
FS
is a regular expression, and how records are separated when
RS
is a regular expression.

If the
FIELDWIDTHS
variable is set to a space separated list of numbers, each field is
expected to have fixed width, and
gawk
splits up the record using the specified widths. The value of
FS
is ignored.
Assigning a new value to
FS
overrides the use of
FIELDWIDTHS,
and restores the default behavior.

Each field in the input record may be referenced by its position,
$1,
$2,
and so on.
$0
is the whole record.
Fields need not be referenced by constants:

n = 5
print $n

prints the fifth field in the input record.

The variable
NF
is set to the total number of fields in the input record.

References to non-existent fields (i.e. fields after
$NF)
produce the null-string. However, assigning to a non-existent field
(e.g.,
$(NF+2) = 5)
increases the value of
NF,
creates any intervening fields with the null string as their value, and
causes the value of
$0
to be recomputed, with the fields being separated by the value of
OFS.
References to negative numbered fields cause a fatal error.
Decrementing
NF
causes the values of fields past the new value to be lost, and the value of
$0
to be recomputed, with the fields being separated by the value of
OFS.

Assigning a value to an existing field
causes the whole record to be rebuilt when
$0
is referenced.
Similarly, assigning a value to
$0
causes the record to be resplit, creating new
values for the fields.

Built-in Variables

Gawk's
built-in variables are:

ARGC

The number of command line arguments (does not include options to
gawk,
or the program source).

ARGIND

The index in
ARGV
of the current file being processed.

ARGV

Array of command line arguments. The array is indexed from
0 to
ARGC
- 1.
Dynamically changing the contents of
ARGV
can control the files used for data.

BINMODE

On non-POSIX systems, specifies use of ``binary'' mode for all file I/O.
Numeric values of 1, 2, or 3, specify that input files, output files, or
all files, respectively, should use binary I/O.
String values of "r", or "w" specify that input files, or output files,
respectively, should use binary I/O.
String values of "rw" or "wr" specify that all files
should use binary I/O.
Any other string value is treated as "rw", but generates a warning message.

CONVFMT

The conversion format for numbers, "%.6g", by default.

ENVIRON

An array containing the values of the current environment.
The array is indexed by the environment variables, each element being
the value of that variable (e.g., ENVIRON["HOME"] might be
/home/arnold).
Changing this array does not affect the environment seen by programs which
gawk
spawns via redirection or the
system()
function.

ERRNO

If a system error occurs either doing a redirection for
getline,
during a read for
getline,
or during a
close(),
then
ERRNO
will contain
a string describing the error.
The value is subject to translation in non-English locales.

FIELDWIDTHS

A white-space separated list of fieldwidths. When set,
gawk
parses the input into fields of fixed width, instead of using the
value of the
FS
variable as the field separator.

FILENAME

The name of the current input file.
If no files are specified on the command line, the value of
FILENAME
is ``-''.
However,
FILENAME
is undefined inside the
BEGIN
block
(unless set by
getline).

FNR

The input record number in the current input file.

FS

The input field separator, a space by default. See
Fields,
above.

IGNORECASE

Controls the case-sensitivity of all regular expression
and string operations. If
IGNORECASE
has a non-zero value, then string comparisons and
pattern matching in rules,
field splitting with
FS,
record separating with
RS,
regular expression
matching with
~
and
!~,
and the
gensub(),
gsub(),
index(),
match(),
split(),
and
sub()
built-in functions all ignore case when doing regular expression
operations.
NOTE:
Array subscripting is
not
affected, nor is the
asort()
function.

Thus, if
IGNORECASE
is not equal to zero,
/aB/
matches all of the strings "ab", "aB", "Ab",
and "AB".
As with all AWK variables, the initial value of
IGNORECASE
is zero, so all regular expression and string
operations are normally case-sensitive.
Under Unix, the full ISO 8859-1 Latin-1 character set is used
when ignoring case.

LINT

Provides dynamic control of the
--lint
option from within an AWK program.
When true,
gawk
prints lint warnings. When false, it does not.
When assigned the string value "fatal",
lint warnings become fatal errors, exactly like
--lint=fatal.
Any other true value just prints warnings.

NF

The number of fields in the current input record.

NR

The total number of input records seen so far.

OFMT

The output format for numbers, "%.6g", by default.

OFS

The output field separator, a space by default.

ORS

The output record separator, by default a newline.

PROCINFO

The elements of this array provide access to information about the
running AWK program.
On some systems,
there may be elements in the array, "group1" through
"groupn" for some
n,
which is the number of supplementary groups that the process has.
Use the
in
operator to test for these elements.
The following elements are guaranteed to be available:

The record terminator.
Gawk
sets
RT
to the input text that matched the character or regular expression
specified by
RS.

RSTART

The index of the first character matched by
match();
0 if no match.
(This implies that character indices start at one.)

RLENGTH

The length of the string matched by
match();
-1 if no match.

SUBSEP

The character used to separate multiple subscripts in array
elements, by default "\034".

TEXTDOMAIN

The text domain of the AWK program; used to find the localized
translations for the program's strings.

Arrays

Arrays are subscripted with an expression between square brackets
([ and ]).
If the expression is an expression list
(expr, expr ...)
then the array subscript is a string consisting of the
concatenation of the (string) value of each expression,
separated by the value of the
SUBSEP
variable.
This facility is used to simulate multiply dimensioned
arrays. For example:

i = "A"; j = "B"; k = "C"
x[i, j, k] = "hello, world\n"

assigns the string "hello, world\n" to the element of the array
x
which is indexed by the string "A\034B\034C". All arrays in AWK
are associative, i.e. indexed by string values.

The special operator
in
may be used in an
if
or
while
statement to see if an array has an index consisting of a particular
value.

if (val in array)
print array[val]

If the array has multiple subscripts, use
(i, j) in array.

The
in
construct may also be used in a
for
loop to iterate over all the elements of an array.

An element may be deleted from an array using the
delete
statement.
The
delete
statement may also be used to delete the entire contents of an array,
just by specifying the array name without a subscript.

Variable Typing And Conversion

Variables and fields
may be (floating point) numbers, or strings, or both. How the
value of a variable is interpreted depends upon its context. If used in
a numeric expression, it will be treated as a number, if used as a string
it will be treated as a string.

To force a variable to be treated as a number, add 0 to it; to force it
to be treated as a string, concatenate it with the null string.

When a string must be converted to a number, the conversion is accomplished
using
strtod(3).
A number is converted to a string by using the value of
CONVFMT
as a format string for
sprintf(3),
with the numeric value of the variable as the argument.
However, even though all numbers in AWK are floating-point,
integral values are
always
converted as integers. Thus, given

CONVFMT = "%2.2f"
a = 12
b = a ""

the variable
b
has a string value of "12" and not "12.00".

Gawk
performs comparisons as follows:
If two variables are numeric, they are compared numerically.
If one value is numeric and the other has a string value that is a
``numeric string,'' then comparisons are also done numerically.
Otherwise, the numeric value is converted to a string and a string
comparison is performed.
Two strings are compared, of course, as strings.
Note that the POSIX standard applies the concept of
``numeric string'' everywhere, even to string constants.
However, this is
clearly incorrect, and
gawk
does not do this.
(Fortunately, this is fixed in the next version of the standard.)

Note that string constants, such as "57", are
not
numeric strings, they are string constants.
The idea of ``numeric string''
only applies to fields,
getline
input,
FILENAME,
ARGV
elements,
ENVIRON
elements and the elements of an array created by
split()
that are numeric strings.
The basic idea is that
user input,
and only user input, that looks numeric,
should be treated that way.

Uninitialized variables have the numeric value 0 and the string value ""
(the null, or empty, string).

Octal and Hexadecimal Constants

Starting with version 3.1 of
gawk ,
you may use C-style octal and hexadecimal constants in your AWK
program source code.
For example, the octal value
011
is equal to decimal
9,
and the hexadecimal value
0x11
is equal to decimal 17.

String Constants

String constants in AWK are sequences of characters enclosed
between double quotes ("). Within strings, certain
escape sequences
are recognized, as in C. These are:

\\

A literal backslash.

\a

The ``alert'' character; usually the ASCIIBEL character.

\b

backspace.

\f

form-feed.

\n

newline.

\r

carriage return.

\t

horizontal tab.

\v

vertical tab.

\xhex digits

The character represented by the string of hexadecimal digits following
the
\x.
As in ANSI C, all following hexadecimal digits are considered part of
the escape sequence.
(This feature should tell us something about language design by committee.)
E.g., "\x1B" is the ASCIIESC (escape) character.

\ddd

The character represented by the 1-, 2-, or 3-digit sequence of octal
digits.
E.g., "\033" is the ASCIIESC (escape) character.

In compatibility mode, the characters represented by octal and
hexadecimal escape sequences are treated literally when used in
regular expression constants. Thus,
/a\52b/
is equivalent to
/a\*b/.

PATTERNS AND ACTIONS

AWK is a line-oriented language. The pattern comes first, and then the
action. Action statements are enclosed in
{
and
}.
Either the pattern may be missing, or the action may be missing, but,
of course, not both. If the pattern is missing, the action is
executed for every single record of input.
A missing action is equivalent to

{ print }

which prints the entire record.

Comments begin with the ``#'' character, and continue until the
end of the line.
Blank lines may be used to separate statements.
Normally, a statement ends with a newline, however, this is not the
case for lines ending in
a ``,'',
{,
?,
:,
&&,
or
||.
Lines ending in
do
or
else
also have their statements automatically continued on the following line.
In other cases, a line can be continued by ending it with a ``\'',
in which case the newline will be ignored.

Multiple statements may
be put on one line by separating them with a ``;''.
This applies to both the statements within the action part of a
pattern-action pair (the usual case),
and to the pattern-action statements themselves.

Patterns

BEGIN
and
END
are two special kinds of patterns which are not tested against
the input.
The action parts of all
BEGIN
patterns are merged as if all the statements had
been written in a single
BEGIN
block. They are executed before any
of the input is read. Similarly, all the
END
blocks are merged,
and executed when all the input is exhausted (or when an
exit
statement is executed).
BEGIN
and
END
patterns cannot be combined with other patterns in pattern expressions.
BEGIN
and
END
patterns cannot have missing action parts.

For
/regular expression/
patterns, the associated statement is executed for each input record that matches
the regular expression.
Regular expressions are the same as those in
egrep(1),
and are summarized below.

A
relational expression
may use any of the operators defined below in the section on actions.
These generally test whether certain fields match certain regular expressions.

The
&&,
||,
and
!
operators are logical AND, logical OR, and logical NOT, respectively, as in C.
They do short-circuit evaluation, also as in C, and are used for combining
more primitive pattern expressions. As in most languages, parentheses
may be used to change the order of evaluation.

The
?:
operator is like the same operator in C. If the first pattern is true
then the pattern used for testing is the second pattern, otherwise it is
the third. Only one of the second and third patterns is evaluated.

The
pattern1, pattern2
form of an expression is called a
range pattern.
It matches all input records starting with a record that matches
pattern1,
and continuing until a record that matches
pattern2,
inclusive. It does not combine with any other sort of pattern expression.

Regular Expressions

Regular expressions are the extended kind found in
egrep.
They are composed of characters as follows:

c

matches the non-metacharacter
c.

\c

matches the literal character
c.

.

matches any character
including
newline.

^

matches the beginning of a string.

$

matches the end of a string.

[abc...]

character list, matches any of the characters
abc....

[^abc...]

negated character list, matches any character except
abc....

r1|r2

alternation: matches either
r1
or
r2.

r1r2

concatenation: matches
r1,
and then
r2.

r+

matches one or more
r's.

r*

matches zero or more
r's.

r?

matches zero or one
r's.

(r)

grouping: matches
r.

r{n}

r{n,}

r{n,m}
One or two numbers inside braces denote an
interval expression.
If there is one number in the braces, the preceding regular expression
r
is repeated
n
times. If there are two numbers separated by a comma,
r
is repeated
n
to
m
times.
If there is one number followed by a comma, then
r
is repeated at least
n
times.

Interval expressions are only available if either
--posix
or
--re-interval
is specified on the command line.

\y

matches the empty string at either the beginning or the
end of a word.

\B

matches the empty string within a word.

\<

matches the empty string at the beginning of a word.

\>

matches the empty string at the end of a word.

\w

matches any word-constituent character (letter, digit, or underscore).

\W

matches any character that is not word-constituent.

\`

matches the empty string at the beginning of a buffer (string).

\'

matches the empty string at the end of a buffer.

The escape sequences that are valid in string constants (see below)
are also valid in regular expressions.

Character classes
are a new feature introduced in the POSIX standard.
A character class is a special notation for describing
lists of characters that have a specific attribute, but where the
actual characters themselves can vary from country to country and/or
from character set to character set. For example, the notion of what
is an alphabetic character differs in the USA and in France.

A character class is only valid in a regular expression
inside
the brackets of a character list. Character classes consist of
[:,
a keyword denoting the class, and
:].
The character
classes defined by the POSIX standard are:

[:alnum:]

Alphanumeric characters.

[:alpha:]

Alphabetic characters.

[:blank:]

Space or tab characters.

[:cntrl:]

Control characters.

[:digit:]

Numeric characters.

[:graph:]

Characters that are both printable and visible.
(A space is printable, but not visible, while an
a
is both.)

[:lower:]

Lower-case alphabetic characters.

[:print:]

Printable characters (characters that are not control characters.)

[:punct:]

Punctuation characters (characters that are not letter, digits,
control characters, or space characters).

[:space:]

Space characters (such as space, tab, and formfeed, to name a few).

[:upper:]

Upper-case alphabetic characters.

[:xdigit:]

Characters that are hexadecimal digits.

For example, before the POSIX standard, to match alphanumeric
characters, you would have had to write
/[A-Za-z0-9]/.
If your character set had other alphabetic characters in it, this would not
match them, and if your character set collated differently from
ASCII, this might not even match the
ASCII alphanumeric characters.
With the POSIX character classes, you can write
/[[:alnum:]]/,
and this matches
the alphabetic and numeric characters in your character set.

Two additional special sequences can appear in character lists.
These apply to non-ASCII character sets, which can have single symbols
(called
collating elements)
that are represented with more than one
character, as well as several characters that are equivalent for
collating,
or sorting, purposes. (E.g., in French, a plain ``e''
and a grave-accented e` are equivalent.)

Collating Symbols

A collating symbol is a multi-character collating element enclosed in
[.
and
.].
For example, if
ch
is a collating element, then
[[.ch.]]
is a regular expression that matches this collating element, while
[ch]
is a regular expression that matches either
c
or
h.

Equivalence Classes

An equivalence class is a locale-specific name for a list of
characters that are equivalent. The name is enclosed in
[=
and
=].
For example, the name
e
might be used to represent all of
``e,'' ``e','' and ``e`.''
In this case,
[[=e=]]
is a regular expression
that matches any of
e,
e',
or
e`.

These features are very valuable in non-English speaking locales.
The library functions that
gawk
uses for regular expression matching
currently only recognize POSIX character classes; they do not recognize
collating symbols or equivalence classes.

The
\y,
\B,
\<,
\>,
\w,
\W,
\`,
and
\'
operators are specific to
gawk;
they are extensions based on facilities in the GNU regular expression libraries.

The various command line options
control how
gawk
interprets characters in regular expressions.

No options

In the default case,
gawk
provide all the facilities of
POSIX regular expressions and the GNU regular expression operators described above.
However, interval expressions are not supported.

--posix

Only POSIX regular expressions are supported, the GNU operators are not special.
(E.g.,
\w
matches a literal
w).
Interval expressions are allowed.

--traditional

Traditional Unix
awk
regular expressions are matched. The GNU operators
are not special, interval expressions are not available, and neither
are the POSIX character classes
([[:alnum:]]
and so on).
Characters described by octal and hexadecimal escape sequences are
treated literally, even if they represent regular expression metacharacters.

--re-interval

Allow interval expressions in regular expressions, even if
--traditional
has been provided.

Actions

Action statements are enclosed in braces,
{
and
}.
Action statements consist of the usual assignment, conditional, and looping
statements found in most languages. The operators, control statements,
and input/output statements
available are patterned after those in C.

Operators

The operators in AWK, in order of decreasing precedence, are

(...)

Grouping

$

Field reference.

++ --

Increment and decrement, both prefix and postfix.

^

Exponentiation (** may also be used, and **= for
the assignment operator).

+ - !

Unary plus, unary minus, and logical negation.

* / %

Multiplication, division, and modulus.

+ -

Addition and subtraction.

space

String concatenation.

< >

<= >=

!= ==
The regular relational operators.

~ !~

Regular expression match, negated match.
NOTE:
Do not use a constant regular expression
(/foo/)
on the left-hand side of a
~
or
!~.
Only use one on the right-hand side. The expression
/foo/ ~ exp
has the same meaning as (($0 ~ /foo/) ~ exp).
This is usually
not
what was intended.

in

Array membership.

&&

Logical AND.

||

Logical OR.

?:

The C conditional expression. This has the form
expr1 ? expr2 : expr3.
If
expr1
is true, the value of the expression is
expr2,
otherwise it is
expr3.
Only one of
expr2
and
expr3
is evaluated.

I/O Statements

Close file, pipe or co-process.
The optional
how
should only be used when closing one end of a
two-way pipe to a co-process.
It must be a string value, either
"to" or "from".

getline

Set
$0
from next input record; set
NF,
NR,
FNR.

getline <file

Set
$0
from next record of
file;
set
NF.

getline var

Set
var
from next input record; set
NR,
FNR.

getline var <file

Set
var
from next record of
file.

command | getline [var]

Run
command
piping the output either into
$0
or
var,
as above.

command |& getline [var]

Run
command
as a co-process
piping the output either into
$0
or
var,
as above.
Co-processes are a
gawk
extension.

next

Stop processing the current input record. The next input record
is read and processing starts over with the first pattern in the
AWK program. If the end of the input data is reached, the
END
block(s), if any, are executed.

nextfile

Stop processing the current input file. The next input record read
comes from the next input file.
FILENAME
and
ARGIND
are updated,
FNR
is reset to 1, and processing starts over with the first pattern in the
AWK program. If the end of the input data is reached, the
END
block(s), if any, are executed.

print

Prints the current record.
The output record is terminated with the value of the
ORS
variable.

print expr-list

Prints expressions.
Each expression is separated by the value of the
OFS
variable.
The output record is terminated with the value of the
ORS
variable.

print expr-list >file

Prints expressions on
file.
Each expression is separated by the value of the
OFS
variable. The output record is terminated with the value of the
ORS
variable.

printf fmt, expr-list

Format and print.

printf fmt, expr-list >file

Format and print on
file.

system(cmd-line)

Execute the command
cmd-line,
and return the exit status.
(This may not be available on non-POSIX systems.)

fflush([file])

Flush any buffers associated with the open output file or pipe
file.
If
file
is missing, then standard output is flushed.
If
file
is the null string,
then all open output files and pipes
have their buffers flushed.

Additional output redirections are allowed for
print
and
printf.

print ... >> file

appends output to the
file.

print ... | command

writes on a pipe.

print ... |& command

sends data to a co-process.

The
getline
command returns 0 on end of file and -1 on an error.
Upon an error,
ERRNO
contains a string describing the problem.

NOTE:
If using a pipe or co-process to
getline,
or from
print
or
printf
within a loop, you
must
use
close()
to create new instances of the command.
AWK does not automatically close pipes or co-processes when
they return EOF.

The printf Statement

The AWK versions of the
printf
statement and
sprintf()
function
(see below)
accept the following conversion specification formats:

%c

An ASCII character.
If the argument used for
%c
is numeric, it is treated as a character and printed.
Otherwise, the argument is assumed to be a string, and the only first
character of that string is printed.

%d, %i

A decimal number (the integer part).

%e , %E

A floating point number of the form
[-]d.dddddde[+-]dd.
The
%E
format uses
E
instead of
e.

%f

A floating point number of the form
[-]ddd.dddddd.

%g , %G

Use
%e
or
%f
conversion, whichever is shorter, with nonsignificant zeros suppressed.
The
%G
format uses
%E
instead of
%e.

Optional, additional parameters may lie between the
%
and the control letter:

count$

Use the
count'th
argument at this point in the formatting.
This is called a
positional specifier
and
is intended primarily for use in translated versions of
format strings, not in the original text of an AWK program.
It is a
gawk
extension.

-

The expression should be left-justified within its field.

space

For numeric conversions, prefix positive values with a space, and
negative values with a minus sign.

+

The plus sign, used before the width modifier (see below),
says to always supply a sign for numeric conversions, even if the data
to be formatted is positive. The
+
overrides the space modifier.

#

Use an ``alternate form'' for certain control letters.
For
%o,
supply a leading zero.
For
%x,
and
%X,
supply a leading
0x
or
0X
for
a nonzero result.
For
%e,
%E,
and
%f,
the result always contains a
decimal point.
For
%g,
and
%G,
trailing zeros are not removed from the result.

0

A leading
0
(zero) acts as a flag, that indicates output should be
padded with zeroes instead of spaces.
This applies even to non-numeric output formats.
This flag only has an effect when the field width is wider than the
value to be printed.

width

The field should be padded to this width. The field is normally padded
with spaces. If the
0
flag has been used, it is padded with zeroes.

.prec

A number that specifies the precision to use when printing.
For the
%e,
%E,
and
%f
formats, this specifies the
number of digits you want printed to the right of the decimal point.
For the
%g,
and
%G
formats, it specifies the maximum number
of significant digits. For the
%d,
%o,
%i,
%u,
%x,
and
%X
formats, it specifies the minimum number of
digits to print. For
%s,
it specifies the maximum number of
characters from the string that should be printed.

The dynamic
width
and
prec
capabilities of the ANSI C
printf()
routines are supported.
A
*
in place of either the
width
or
prec
specifications causes their values to be taken from
the argument list to
printf
or
sprintf().
To use a positional specifier with a dynamic width or precision,
supply the
count$
after the
*
in the format string.
For example, "%3$*2$.*1$s".

Special File Names

When doing I/O redirection from either
print
or
printf
into a file,
or via
getline
from a file,
gawk
recognizes certain special filenames internally. These filenames
allow access to open file descriptors inherited from
gawk's
parent process (usually the shell).
These file names may also be used on the command line to name data files.
The filenames are:

/dev/stdin

The standard input.

/dev/stdout

The standard output.

/dev/stderr

The standard error output.

/dev/fd/n

The file associated with the open file descriptor
n.

These are particularly useful for error messages. For example:

print "You blew it!" > "/dev/stderr"

whereas you would otherwise have to use

print "You blew it!" | "cat 1>&2"

The following special filenames may be used with the
|&
co-process operator for creating TCP/IP network connections.

/inet/tcp/lport/rhost/rport

File for TCP/IP connection on local port
lport
to
remote host
rhost
on remote port
rport.
Use a port of
0
to have the system pick a port.

/inet/udp/lport/rhost/rport

Similar, but use UDP/IP instead of TCP/IP.

/inet/raw/lport/rhost/rport

Reserved for future use.

Other special filenames provide access to information about the running
gawk
process.
These filenames are now obsolete.
Use the
PROCINFO
array to obtain the information they provide.
The filenames are:

/dev/pid

Reading this file returns the process ID of the current process,
in decimal, terminated with a newline.

/dev/ppid

Reading this file returns the parent process ID of the current process,
in decimal, terminated with a newline.

/dev/pgrpid

Reading this file returns the process group ID of the current process,
in decimal, terminated with a newline.

/dev/user

Reading this file returns a single record terminated with a newline.
The fields are separated with spaces.
$1
is the value of the
getuid(2)
system call,
$2
is the value of the
geteuid(2)
system call,
$3
is the value of the
getgid(2)
system call, and
$4
is the value of the
getegid(2)
system call.
If there are any additional fields, they are the group IDs returned by
getgroups(2).
Multiple groups may not be supported on all systems.

Numeric Functions

AWK has the following built-in arithmetic functions:

atan2(y, x)

Returns the arctangent of
y/x
in radians.

cos(expr)

Returns the cosine of
expr,
which is in radians.

exp(expr)

The exponential function.

int(expr)

Truncates to integer.

log(expr)

The natural logarithm function.

rand()

Returns a random number between 0 and 1.

sin(expr)

Returns the sine of
expr,
which is in radians.

sqrt(expr)

The square root function.

srand([expr])

Uses
expr
as a new seed for the random number generator. If no
expr
is provided, the time of day is used.
The return value is the previous seed for the random
number generator.

String Functions

Gawk
has the following built-in string functions:

asort(s [, d])

Returns the number of elements in the source
array
s.
The contents of
s
are sorted using
gawk's
normal rules for
comparing values, and the indexes of the
sorted values of
s
are replaced with sequential
integers starting with 1. If the optional
destination array
d
is specified, then
s
is first duplicated into
d,
and then
d
is sorted, leaving the indexes of the
source array
s
unchanged.

gensub(r, s, h [, t])

Search the target string
t
for matches of the regular expression
r.
If
h
is a string beginning with
g
or
G,
then replace all matches of
r
with
s.
Otherwise,
h
is a number indicating which match of
r
to replace.
If
t
is not supplied,
$0
is used instead.
Within the replacement text
s,
the sequence
\n,
where
n
is a digit from 1 to 9, may be used to indicate just the text that
matched the
n'th
parenthesized subexpression. The sequence
\0
represents the entire matched text, as does the character
&.
Unlike
sub()
and
gsub(),
the modified string is returned as the result of the function,
and the original target string is
not
changed.

gsub(r, s [, t])

For each substring matching the regular expression
r
in the string
t,
substitute the string
s,
and return the number of substitutions.
If
t
is not supplied, use
$0.
An
&
in the replacement text is replaced with the text that was actually matched.
Use
\&
to get a literal
&.
(This must be typed as "\\&";
see GAWK: Effective AWK Programming
for a fuller discussion of the rules for
&'s
and backslashes in the replacement text of
sub(),
gsub(),
and
gensub().)

index(s, t)

Returns the index of the string
t
in the string
s,
or 0 if
t
is not present.
(This implies that character indices start at one.)

length([s])

Returns the length of the string

s,
or the length of
$0
if
s
is not supplied.

match(s, r [, a])

Returns the position in
s
where the regular expression
r
occurs, or 0 if
r
is not present, and sets the values of
RSTART
and
RLENGTH.
Note that the argument order is the same as for the
~
operator:
str ~re.
If array
a
is provided,
a
is cleared and then elements 1 through
n
are filled with the portions of
s
that match the corresponding parenthesized
subexpression in
r.
The 0'th element of
a
contains the portion
of
s
matched by the entire regular expression
r.

split(s, a [, r])

Splits the string
s
into the array
a
on the regular expression
r,
and returns the number of fields. If
r
is omitted,
FS
is used instead.
The array
a
is cleared first.
Splitting behaves identically to field splitting, described above.

sprintf(fmt, expr-list)

Prints
expr-list
according to
fmt,
and returns the resulting string.

strtonum(str)

Examines
str,
and returns its numeric value.
If
str
begins
with a leading
0,
strtonum()
assumes that
str
is an octal number.
If
str
begins
with a leading
0x
or
0X,
strtonum()
assumes that
str
is a hexadecimal number.

sub(r, s [, t])

Just like
gsub(),
but only the first matching substring is replaced.

substr(s, i [, n])

Returns the at most
n-character
substring of
s
starting at
i.
If
n
is omitted, the rest of
s
is used.

tolower(str)

Returns a copy of the string
str,
with all the upper-case characters in
str
translated to their corresponding lower-case counterparts.
Non-alphabetic characters are left unchanged.

toupper(str)

Returns a copy of the string
str,
with all the lower-case characters in
str
translated to their corresponding upper-case counterparts.
Non-alphabetic characters are left unchanged.

Time Functions

Since one of the primary uses of AWK programs is processing log files
that contain time stamp information,
gawk
provides the following functions for obtaining time stamps and
formatting them.

mktime(datespec)

Rurns
datespec
into a time stamp of the same form as returned by
systime().
The
datespec
is a string of the form
YYYY MM DD HH MM SS[ DST].
The contents of the string are six or seven numbers representing respectively
the full year including century,
the month from 1 to 12,
the day of the month from 1 to 31,
the hour of the day from 0 to 23,
the minute from 0 to 59,
and the second from 0 to 60,
and an optional daylight saving flag.
The values of these numbers need not be within the ranges specified;
for example, an hour of -1 means 1 hour before midnight.
The origin-zero Gregorian calendar is assumed,
with year 0 preceding year 1 and year -1 preceding year 0.
The time is assumed to be in the local timezone.
If the daylight saving flag is positive,
the time is assumed to be daylight saving time;
if zero, the time is assumed to be standard time;
and if negative (the default),
mktime()
attempts to determine whether daylight saving time is in effect
for the specified time.
If
datespec
does not contain enough elements or if the resulting time
is out of range,
mktime()
returns -1.

strftime([format [, timestamp]])

Formats
timestamp
according to the specification in
format.
The
timestamp
should be of the same form as returned by
systime().
If
timestamp
is missing, the current time of day is used.
If
format
is missing, a default format equivalent to the output of
date(1)
is used.
See the specification for the
strftime()
function in ANSI C for the format conversions that are
guaranteed to be available.
A public-domain version of
strftime(3)
and a man page for it come with
gawk;
if that version was used to build
gawk,
then all of the conversions described in that man page are available to
gawk.

systime()

Returns the current time of day as the number of seconds since the Epoch
(1970-01-01 00:00:00 UTC on POSIX systems).

Bit Manipulations Functions

Starting with version 3.1 of
gawk,
the following bit manipulation functions are available.
They work by converting double-precision floating point
values to
unsigned long
integers, doing the operation, and then converting the
result back to floating point.
The functions are:

and(v1, v2)

Return the bitwise AND of the values provided by
v1
and
v2.

compl(val)

Return the bitwise complement of
val.

lshift(val, count)

Return the value of
val,
shifted left by
count
bits.

or(v1, v2)

Return the bitwise OR of the values provided by
v1
and
v2.

rshift(val, count)

Return the value of
val,
shifted right by
count
bits.

xor(v1, v2)

Return the bitwise XOR of the values provided by
v1
and
v2.

Internationalization Functions

Starting with version 3.1 of
gawk,
the following functions may be used from within your AWK program for
translating strings at run-time.
For full details, see GAWK: Effective AWK Programming.

bindtextdomain(directory [, domain])

Specifies the directory where
gawk
looks for the
.mo
files, in case they
will not or cannot be placed in the ``standard'' locations
(e.g., during testing).
It returns the directory where
domain
is ``bound.''

The default
domain
is the value of
TEXTDOMAIN.
If
directory
is the null string (""), then
bindtextdomain()
returns the current binding for the
given
domain.

dcgettext(string [, domain [, category]])

Returns the translation of
string
in
text domain
domain
for locale category
category.
The default value for
domain
is the current value of
TEXTDOMAIN.
The default value for
category
is "LC_MESSAGES".

If you supply a value for
category,
it must be a string equal to
one of the known locale categories described
in GAWK: Effective AWK Programming.
You must also supply a text domain. Use
TEXTDOMAIN
if you want to use the current domain.

dcngettext(string1 , string2 , number [, domain [, category]])

Returns the plural form used for
number
of the translation of
string1
and
string2
in
text domain
domain
for locale category
category.
The default value for
domain
is the current value of
TEXTDOMAIN.
The default value for
category
is "LC_MESSAGES".

If you supply a value for
category,
it must be a string equal to
one of the known locale categories described
in GAWK: Effective AWK Programming.
You must also supply a text domain. Use
TEXTDOMAIN
if you want to use the current domain.

USER-DEFINED FUNCTIONS

Functions in AWK are defined as follows:

function name(parameter list) { statements }

Functions are executed when they are called from within expressions
in either patterns or actions. Actual parameters supplied in the function
call are used to instantiate the formal parameters declared in the function.
Arrays are passed by reference, other variables are passed by value.

Since functions were not originally part of the AWK language, the provision
for local variables is rather clumsy: They are declared as extra parameters
in the parameter list. The convention is to separate local variables from
real parameters by extra spaces in the parameter list. For example:

The left parenthesis in a function call is required
to immediately follow the function name,
without any intervening white space.
This is to avoid a syntactic ambiguity with the concatenation operator.
This restriction does not apply to the built-in functions listed above.

Functions may call each other and may be recursive.
Function parameters used as local variables are initialized
to the null string and the number zero upon function invocation.

Use
return expr
to return a value from a function. The return value is undefined if no
value is provided, or if the function returns by ``falling off'' the
end.

If
--lint
has been provided,
gawk
warns about calls to undefined functions at parse time,
instead of at run time.
Calling an undefined function at run time is a fatal error.

The word
func
may be used in place of
function.

DYNAMICALLY LOADING NEW FUNCTIONS

Beginning with version 3.1 of
gawk,
you can dynamically add new built-in functions to the running
gawk
interpreter.
The full details are beyond the scope of this manual page;
see GAWK: Effective AWK Programming for the details.

extension(object, function)

Dynamically link the shared object file named by
object,
and invoke
function
in that object, to perform initialization.
These should both be provided as strings.
Returns the value returned by
function.

This function is provided and documented in GAWK: Effective AWK Programming,
but everything about this feature is likely to change
in the next release.
We STRONGLY recommend that you do not use this feature
for anything that you aren't willing to redo.

SIGNALS

pgawk
accepts two signals.
SIGUSR1
causes it to dump a profile and function call stack to the
profile file, which is either
awkprof.out,
or whatever file was named with the
--profile
option. It then continues to run.
SIGHUP
causes it to dump the profile and function call stack and then exit.

EXAMPLES

Print and sort the login names of all users:
BEGIN { FS = ":" }
{ print $1 | "sort" }
Count lines in a file:
{ nlines++ }
END { print nlines }
Precede each line by its number in the file:
{ print FNR, $0 }
Concatenate and line number (a variation on a theme):
{ print NR, $0 }

INTERNATIONALIZATION

String constants are sequences of characters enclosed in double
quotes. In non-English speaking environments, it is possible to mark
strings in the AWK program as requiring translation to the native
natural language. Such strings are marked in the AWK program with
a leading underscore (``_''). For example,

gawk 'BEGIN { print "hello, world" }'

always prints
hello, world.
But,

gawk 'BEGIN { print _"hello, world" }'

might print
bonjour, monde
in France.

There are several steps involved in producing and running a localizable
AWK program.

1.

Add a
BEGIN
action to assign a value to the
TEXTDOMAIN
variable to set the text domain to a name associated with your program.

BEGIN { TEXTDOMAIN = "myprog" }

This allows
gawk
to find the
.mo
file associated with your program.
Without this step,
gawk
uses the
messages
text domain,
which likely does not contain translations for your program.

2.

Mark all strings that should be translated with leading underscores.

3.

If necessary, use the
dcgettext()
and/or
bindtextdomain()
functions in your program, as appropriate.

The internationalization features are described in full detail in GAWK: Effective AWK Programming.

POSIX COMPATIBILITY

A primary goal for
gawk
is compatibility with the POSIX standard, as well as with the
latest version of UNIXawk.
To this end,
gawk
incorporates the following user visible
features which are not described in the AWK book,
but are part of the Bell Laboratories version of
awk,
and are in the POSIX standard.

The book indicates that command line variable assignment happens when
awk
would otherwise open the argument as a file, which is after the
BEGIN
block is executed. However, in earlier implementations, when such an
assignment appeared before any file names, the assignment would happen
before
the
BEGIN
block was run. Applications came to depend on this ``feature.''
When
awk
was changed to match its documentation, the
-v
option for assigning variables before program execution was added to
accommodate applications that depended upon the old behavior.
(This feature was agreed upon by both the Bell Laboratories and the GNU developers.)

The
-W
option for implementation specific features is from the POSIX standard.

When processing arguments,
gawk
uses the special option ``--'' to signal the end of
arguments.
In compatibility mode, it warns about but otherwise ignores
undefined options.
In normal operation, such arguments are passed on to the AWK program for
it to process.

The AWK book does not define the return value of
srand().
The POSIX standard
has it return the seed it was using, to allow keeping track
of random number sequences. Therefore
srand()
in
gawk
also returns its current seed.

Other new features are:
The use of multiple
-f
options (from MKS
awk);
the
ENVIRON
array; the
\a,
and
\v
escape sequences (done originally in
gawk
and fed back into the Bell Laboratories version); the
tolower()
and
toupper()
built-in functions (from the Bell Laboratories version); and the ANSI C conversion specifications in
printf
(done first in the Bell Laboratories version).

HISTORICAL FEATURES

There are two features of historical AWK implementations that
gawk
supports.
First, it is possible to call the
length()
built-in function not only with no argument, but even without parentheses!
Thus,

a = length# Holy Algol 60, Batman!

is the same as either of

a = length()
a = length($0)

This feature is marked as ``deprecated'' in the POSIX standard, and
gawk
issues a warning about its use if
--lint
is specified on the command line.

The other feature is the use of either the
continue
or the
break
statements outside the body of a
while,
for,
or
do
loop. Traditional AWK implementations have treated such usage as
equivalent to the
next
statement.
Gawk
supports this usage if
--traditional
has been specified.

GNU EXTENSIONS

Gawk
has a number of extensions to POSIXawk.
They are described in this section. All the extensions described here
can be disabled by
invoking
gawk
with the
--traditional
option.

The following features of
gawk
are not available in
POSIXawk.

*

No path search is performed for files named via the
-f
option. Therefore the
AWKPATH
environment variable is not special.

*

The
\x
escape sequence.
(Disabled with
--posix.)

*

The
fflush()
function.
(Disabled with
--posix.)

*

The ability to continue lines after
?
and
:.
(Disabled with
--posix.)

*

Octal and hexadecimal constants in AWK programs.

*

The
ARGIND,
BINMODE,
ERRNO,
LINT,
RT
and
TEXTDOMAIN
variables are not special.

*

The
IGNORECASE
variable and its side-effects are not available.

*

The
FIELDWIDTHS
variable and fixed-width field splitting.

*

The
PROCINFO
array is not available.

*

The use of
RS
as a regular expression.

*

The special file names available for I/O redirection are not recognized.

*

The
|&
operator for creating co-processes.

*

The ability to split out individual characters using the null string
as the value of
FS,
and as the third argument to
split().

Adding new built-in functions dynamically with the
extension()
function.

The AWK book does not define the return value of the
close()
function.
Gawk's
close()
returns the value from
fclose(3),
or
pclose(3),
when closing an output file or pipe, respectively.
It returns the process's exit status when closing an input pipe.
The return value is -1 if the named file, pipe
or co-process was not opened with a redirection.

When
gawk
is invoked with the
--traditional
option,
if the
fs
argument to the
-F
option is ``t'', then
FS
is set to the tab character.
Note that typing
gawk -F\t ...
simply causes the shell to quote the ``t,'', and does not pass
``\t'' to the
-F
option.
Since this is a rather ugly special case, it is not the default behavior.
This behavior also does not occur if
--posix
has been specified.
To really get a tab character as the field separator, it is best to use
single quotes:
gawk -F'\t' ....